Limited effects of long-term n-3 or n-6 PUFA supplementation combined with varying dietary protein levels on five distinct fat depots in pigs

Feeding pigs a reduced crude protein diet has proven to be an important tool for improving meat quality, but the effects of low- or high-protein diets on fat deposits in pigs are less well understood. The objective of this study was to investigate the effects of n -3 and n -6 PUFA supplementation combined with reduced-protein diet (RPD) or high-protein diet (HPD) on lipid metabolism in five distinct fat depots in pigs. A total of 40 castrated male Landrace pigs were divided into four experimental groups fed diets differing in protein levels and PUFA supplementation and one control group. The n -3 and n -6 PUFA-supplemented RPD/HPD resulted in significant changes, primarily in the n -3 and n -6 PUFA concentrations in the adipose depots of the pigs (P <0.05). Compared with the control group, the content of the most abundant fatty acid in adipose tissue, oleic acid, was significantly decreased in the back, intestinal, and perirenal fat of almost all experimental groups. The gene expression of lipogenic enzymes (ELOVL5, FADS1, FADS2, SREBP1, ACACA, FASN, and SCD) at the mRNA level did not change in response to the different diets in any of the fat depots. However, ACACA and FASN protein expression in perirenal fat and SREBP expression in back fat were affected by diet (P <0.05). On the basis of the very limited dietary effects observed on fat depots in Landrace pigs, our results suggest that lipid metabolism remains similar regardless of whether different amounts of dietary protein are combined with n -3 or n -6 PUFA supplementation.